Apparatus and methods for burning waste, and waste slurries

ABSTRACT

Burners for burning waste, comprising a conventional fuel nozzle and a waste slurry nozzle. Waste slurry nozzles, comprising a first conduit, a second conduit and an acceleration zone comprising a mixing chamber and an acceleration conduit. Waste slurries comprising a continuous phase and a solids phase, the solids phase consisting essentially of solids having at least one dimension less than about 1/8 inch and solids having no dimension less than 1/8 inch and no dimension larger than about 5/8 inch. Methods for burning waste, comprising feeding a slurry of cement raw materials to an up end of a rotating kiln, and ejecting a waste slurry from a burner such that a portion of the waste slurry lands in the calcining zone of the kiln.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to kilns, to nozzles for kilns, and towaste slurries, more particularly, to methods of burning waste slurriesin cement kilns, and to waste slurries, kilns and kiln nozzles for usein such methods. The present invention is especially useful inconnection with waste slurries containing hazardous waste.

2. Description of the Prior Art

Many types of solid combustible waste generated by industry andelsewhere are categorized as hazardous waste because of, e.g., theirflammable or toxic characteristics. Recent environmental regulationshave imposed strict restrictions on disposal of hazardous waste,frequently making it necessary to employ expensive high-temperatureincinerators with extentive emission control devices.

Cement kilns have received favorable review from federal and stateenvironmental regulatory agencies as providing ideal conditions fordisposal of combustible waste materials. Not only does the burning ofhazardous waste in operating kilns allow for recovery of energy valuesfrom hazardous waste, but also, because of their high operatingtemperatures, long residence time and ability to provide favorableconditions for chemical combination of inorganic residues into theactive components of cement, such operations provide excellentconditions for environmentally sound disposal of combustible hazardouswaste.

The burning of hazardous waste, however, faces a number of practicallimitations. Before the promulgation of existing EPA air qualityregulations, it was a practice to charge combustible solid waste intothe cold end of cement kilns with the mineral materials being processedinto cement. With current regulations, however, it would be impossibleto follow such practices. Combustible hazardous waste contains manyvolatile organic substances, which would result in unacceptablehydrocarbon emissions because the volatile components are driven offinto effluent gases at temperatures below those required for thermaldegradation of the volatilized components.

One attempt to provide a system in which hazardous waste can be burnedin a cement kiln is disclosed in U.S. Pat. No. 4,974,529. In accordancewith the method disclosed in that patent, hazardous waste iscontainerized and fed into a kiln through a port formed in the kilnwall, the port being aligned with a drop tube inside the kiln. Hazardouswaste fuel is delivered to the kiln through the port at predeterminedtimes during operation of the kiln. This method is inconvenient andcomplicates the design of kilns, and it requires introduction of thefuel in uneven pulses.

U.S. Pat. No. 4,806,056 discloses an apparatus and a method for usingmaterials such as coarse pieces of pneumatic tire casings as a secondarysource of heat energy in applications such as lime kilns, cement kilns,boiler furnaces and the like. Hazardous waste sludges can be metered tomix and coat the surfaces of tire-derived fuel so that the hazardousmaterials can be fed into a cement kiln. The patent notes that in orderto dispose of some hazardous wastes safely, it is necessary to exposethem to sufficiently high temperatures for long enough periods of time.According to the patent, for delivery of tire-derived fuel for use incement kilns and lime kilns, it is preferred to deliver the fuelpneumatically through a large pipe, the size of which must be adequateto permit passage of the pieces of tire-derived fuel without beingclogged. Referring to FIG. 6, air is fed through an exit mouth 64 to afuel delivery conduit 54, taking along with it comminuted tire-derivedfuel 48 delivered through an infeed conduit 56. In one preferredapplication, shown in FIG. 8, the stream of air and tire-derived fuelproceeds through nozzle 70 and is discharged into the combustion chamberof a lime kiln 72.

U.S. Pat. No. 4,976,210 discloses a method and apparatus for treatinghazardous waste materials in which bulk material such as heavy solidhazardous waste material is supplied via a hopper to a hydraulic ram 28(see FIG. 1) or is supplied via a flow line and pumped into the intake18 of the kiln.

SUMMARY OF THE INVENTION

One object of the present invention is to provide apparatus and methodswhich can be used to efficiently burn waste material in a cement kilnwithout having adverse effects on the cement or on the environment.

Another object of the present invention is to provide waste slurrieswhich can be efficiently burned using such apparatus.

Another object is to provide a method of conveying combustible solidsinto an area of the kiln where complete combustion may result in formingan intermediate char, then oxidation of the fixed carbon withoutdetrimental consequences in the local and temporary reducing atmosphere.

In accordance with the present invention, there are provided wasteslurries comprising a continuous phase and a solids phase, the solidsphase consisting essentially of solids having at least one dimensionless than about 1/8 inch and solids having no dimension less than 1/8inch and no dimension larger than about 5/8 inch.

In addition, there are provided methods for burning waste, comprising:

feeding a slurry of cement raw materials to an up end of a rotating kilnhaving the up end and a down end, a calcining zone between the up endand the down end and a clinkering zone between the calcining zone andthe down end; and

ejecting a waste slurry from a burner at the down end into theclinkering zone such that a portion of the waste slurry lands in thecalcining zone.

There are also provided methods of injecting solid waste into a kiln byadding the solid waste to liquid flowing to a pump intake and using theliquid to convey the solid waste, and burning in suspension solid wastewhich has at least one dimension less than about 1/8 inch and burningsolid waste having all dimensions greater than 1/8 inch in a calciningzone of the kiln.

There are also provided burners for burning waste, comprising aconventional fuel nozzle and a waste slurry nozzle.

There are also provided waste slurry nozzles, comprising:

a first conduit having an inlet and an outlet, a second conduit havingan entrance and an exit; an acceleration zone comprising a mixingchamber and an acceleration conduit, the mixing chamber having an intakeend and a release end, the acceleration conduit having a receiving endand a discharge end, the intake end of the mixing chamber communicatingwith the outlet of the first conduit and the exit of the second conduit,the release end of the mixing chamber communicating with the receivingend of the acceleration conduit.

The invention may be more fully understood with reference to theaccompanying drawings and the following description of the embodimentsshown in those drawings. The invention is not limited to the exemplaryembodiments and should be recognized as contemplating all modificationswithin the skill of an ordinary artisan.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a waste burning system in accordancewith the present invention.

FIG. 2 is an enlarged view of the waste slurry nozzle 16 depicted inFIG. 1.

FIG. 3 is a cross-sectional view of a preferred burner in accordancewith a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of a pipe grinder used in accordancewith a preferred aspect of the present invention.

FIGS. 5 and 6 are front views of discs in the pipe grinder depicted inFIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with one aspect of the present invention, there isprovided a system which can employ a conventional cement kiln (either a"wet" type or a "dry" type) in a method which uses hazardous and/ornon-hazardous waste to provide part of the fuel requirement. The term"waste" is used herein to mean by-products of a process, suchby-products being of a nature that the operator of the process desiresto dispose of them. This invention is particularly adapted to employinghazardous waste. The phrase "hazardous waste" is defined herein inaccordance with prevailing governmental codes. Under current prevailingcodes, materials such as sludges from sewage treatment mills, foodprocessing waste materials, pulp and paper industry waste material andrubber wastes are all non-hazardous waste materials. Refinery oil/waterseparator sludges may or may not contain hazardous waste.

Conventional cement kilns are typically large inclined cylinders, intothe "up" end of which cement raw materials are fed. The cement rawmaterials go through physical and chemical changes as they pass throughthe kiln from the up end to the "down" end, where they are discharged ashot lava material (clinker) into a cooler and recovered. A burner ispositioned in the down end of the kiln to provide very high temperatureswithin the kiln. Hot gases travel counter-current relative to the cementraw material, from the down end of the kiln to the up end. The presentinvention provides a system whereby waste, especially hazardous waste,can be used as part of the fuel being burned by the burner withoutdegrading the quality of the clinker, without having environmentallyunacceptable effluent and without damaging the kiln.

FIG. 1 depicts a system in accordance with the present invention, thesystem employing a conventional "wet" cement kiln comprising a largecylindrical kiln 10. The present invention is equally applicable to asystem in which there is employed a "dry" cement kiln, i.e., a kilnwhich includes an apparatus for preheating or precalcining the mineralmaterial.

A suitable size for the cylinder depicted in FIG. 1 is a diameter in therange of from about 11 to about 14 feet and a length of from about 350to about 500 feet. Raw cement materials are fed into the up end of thekiln as an aqueous slurry containing raw materials suitable for makingcement. The aqueous slurry preferably contains limestone, water, sand,clay, shale, and/or any other material(s) suitable for making cement.The aqueous slurry preferably contains from about 14 to about 18 weightpercent, most preferably about 16 weight percent, solids. Gases passingin the opposite direction are at a temperature on the order of about575° F. at the up end of the kiln 10. The kiln 10 is continuouslyrotated at a rate of from about 1 to about 2 rotations per minute.

As the cement slurry begins to pass through the kiln 10 toward the downend, it enters a chain gate section 11 where large chains resemblinglight-weight naval anchor chain and of lengths approximately equal tothe diameter of the kiln 10 are attached around the entire circumferenceof the kiln 10. As the kiln 10 rotates, the chains become coated withthe cement slurry, rise to the top of the kiln 10 and provide a largesurface area for heat exchange and mass exchange. At the down end of thechain gate section 11, as a result of evaporation in the chain gatesection 11, the cement slurry is substantially free of non-chemicallybound water, and is at a temperature on the order of about 500° F. Thegases passing in the opposite direction are at a temperature on theorder of about 1000° F. at the down end of the chain gate section 11.

As the cement material continues passing through the kiln 10, it nextenters a calcining zone 12. The calcining zone 12 is a severeendothermic zone. The cement material includes a high percentage ofcalcium carbonate, so that waters of crystallization, water of hydrationand carbon dioxide are driven off to produce anhydrous material which isthen at a temperature on the order of about 2250° F. The gases passingthrough the calcining zone 12 in the opposite direction are at atemperature on the order of from about 1400° F. to about 2300° F.

The anhydrous cement material next passes into a clinkering zone 13,where it melts and coats the walls of the rotating kiln 10. The cementmaterial is exothermic, chemically active, and at a temperature on theorder of from about 2650° F. to about 2700° F. The cement materialcrystallizes at the end of the exotherm and is discharged from the downend of the kiln 10 as a hot crystallized lava material (clinker).

From the down end of the kiln 10, the clinker drops down into one ormore clinker coolers 14 in which it is cooled by heat exchange with airdriven by any suitable means, such as by a fan, the air passing in theopposite direction through the clinker cooler(s) 14. The cooled clinkeris recovered and the air heated in the clinker cooler(s) 14 is passedinto the kiln 10 where it is used as secondary air for combustion insidethe kiln 10. The secondary air is at a temperature on the order of fromabout 900° F. to about 1700° F., typically about 1400° F.

A burner 15 fires into the secondary air from the clinker cooler(s) 14in a direction opposite to the direction in which the cement slurrymoves through the kiln 10. In the embodiment shown in FIG. 1, the burnerconsists of two fuel outlets positioned side-by-side and aligned suchthat their axes intersect a short distance into the kiln 10 from thedown end of the kiln 10. Those two fuel outlets are a waste slurrynozzle 16 and a conventional fuel nozzle 17. The waste slurry nozzle 16is preferably positioned such that the stream flowing therefrom impingesthe flame emanating from the conventional fuel nozzle 17. In accordancewith a second embodiment in accordance with the present invention, thewaste slurry nozzle 116 and the conventional fuel nozzle 117 arearranged substantially coaxially, as depicted in FIG. 3, with theconventional fuel nozzle 117 surrounding the waste slurry nozzle 116.

The fuel supplied to the conventional fuel nozzle 17 can comprise anysuitable conventional fuel, preferably a moderate BTU material, such ascoal (e.g., lignite), petroleum coke, waste dry fuel and the like.

The waste slurry in accordance with the present invention has acontinuous phase and a solids phase. The continuous phase may includeair and/or conventional liquid fuel used in cement kilns. When using airas the continuous phase, the flow of air is preferably from about 50 toabout 225 weight percent, based on the amount of solids phase, morepreferably from about 125 to about 150 weight percent. When using air asthe continuous phase, at least about 50%, typically about 75%, of thewaste slurry burns in suspension (in the flame emanating from theburner). When using a liquid as the continuous phase, the liquid(s)(e.g., waste hydrocarbons, waste liquids containing combustible hydrogenand carbon, waste fuels, hydrocarbon solvents and petroleum oils) haveabout 10 to about 20 weight percent of dissolved or suspended solid orsemi-solid material such as oils, greases, resins, adhesives, and thelike ground up very small. The solid material particle size for thecontinuous phase is colloidal to the extent possible and is ofrelatively low viscosity, i.e., between about 100 centipoise and about500 centipoise, however, higher viscosity up to 10,000 centipoise can beused. The solids phase of the waste slurry in accordance with thepresent invention can include two types of solids. The first type ofsolids is shredded solids which have at least one dimension which isless than about 1/8 inch. Such solids can include plastics, such asplastic containers, visqueen dripcloths, respirator cartridges, spentsafety clothing (e.g., boots, gloves, Tyvek® suits), and can includeother materials, such as small paint containers with their contents(e.g., pint paint cans), semi-solid paint heels or skins from the topsof containers, semi-solid adhesives, resins and copolymers that areeither fully or partially reacted, epoxies, urethanes, acrylics,polyesters, and/or any other type of plastic or polymer material. Thesecond type of solids that can be present in the solids phase inaccordance with the present invention includes solids which have nodimension less than 1/8 inch and no dimension larger than 5/8 inch. Suchmaterials can include ground, fully-reacted resins, cured paint rimsfrom plastics drums (e.g., a 55 gallon plastic drum) which have beenshredded, clean-up material, plastic, wood, carbon, agglomeratedmaterials, etc. Such materials are typically roughly spherical.

The waste slurry nozzle 16 and the conventional fuel nozzle 17 are madeof a material which can withstand the high temperatures within the kiln10. An especially preferred material for their construction is stainlesssteel.

The shape of the conventional fuel nozzle 17 can be any suitable shapewhich effectively provides the desired flow rate of conventional fuel tothe kiln 10. Desired flow rates for the conventional fuel depend onseveral factors, as discussed below.

The shape of the waste slurry nozzle 16 is critically important tooperation in accordance with the present invention for several reasons.

First, the flame emanating from the burner 15 must be very long andnarrow, extending at least about 70 feet long so that it extends to theexothermic zone without impinging on the walls of the kiln 10. In theexothermic zone, the cement material coats the walls of the kiln 10which transmits enough heat through the cement material that itcrystallizes against the walls of the kiln 10. If the heat in thatregion is increased, the cement material coating on the walls of thekiln 10 becomes thinner, and the flame will eventually impinge andabrade the walls. If that region becomes cooler, the cement materialcoating will become thicker and build up a ring which will restrict orprevent movement of the cement material through the kiln 10.

Second, any solids which are not burned in suspension in the flame mustbe accelerated to a high enough velocity that they fly out the end ofthe flame and land in the calcining zone 12, where they are burned. Inorder to reach the calcining zone, such solids must travel from about 70to about 200 feet, for example, about 120 feet. The substantiallyspherical solids which have no dimension less than 1/8 inch and nodimension larger than 5/8 inch typically are incapable of being burnt insuspension. After such solids go through the flame, they produce piecesof char or fixed carbon, a very powerful reducing material resemblingcoke in a blast furnace. If these solids land in the clinkering zone 13,they tend to reduce the clinker, thereby causing the clinker to beunacceptably discolored. The remainder of the material in the wasteslurry, i e., any liquid in the continuous phase, the fine particulateand the particulate material having at least one dimension that is onthe order of 1/8 inch or smaller, generally all burn in suspension inthe flame.

Third, the waste slurry nozzle 16 must be able to pass all of the solidscontained in the waste slurry without plugging up, even when operatingat relatively low flow rates and pressures.

The waste slurry nozzle 16 of the embodiment depicted in FIG. 1 is shownin an enlarged view in FIG. 2, and it comprises a substantiallycylindrical waste conduit 18, a substantially cylindrical air conduit19, a mixing chamber 20 and a substantially cylindrical accelerationconduit 21. An air inlet 22 is formed in the air conduit 19 and a wasteslurry inlet 23 is formed in the waste conduit 18. The waste conduit 18and the acceleration conduit 21 are substantially coaxial. In theembodiment shown in FIG. 2, the waste conduit 18 is positioned withinthe air conduit 19 and has an axis parallel to the axis of the airconduit 19. The mixing chamber 20 communicates on its intake end withboth the waste conduit 18 and the air conduit 19, and on its release endwith the acceleration conduit 21. The mixing chamber 20 tapersrelatively gradually, preferably such that the ratio of the differencebetween the cross-sectional areas of the intake end and the release endof the mixing chamber 20, divided by the distance between the intake endand the release end of the mixing chamber 20, is in the range of fromabout 0.5 to about 2.0, and is preferably about 1.0. The length of theacceleration zone, which includes the mixing chamber 20 and theacceleration conduit 21, is critically important, and preferably is inthe range of from about 10 to about 30 times the diameter of theacceleration conduit 21. The length of the waste slurry conduit 18 andthe length of the air conduit 19 must be sufficient to position the endof the acceleration conduit 21 at the desired location within the kiln10.

The solids phase of the waste slurry can be fed to the waste conduit 18by any suitable means and at any appropriate location. One preferred wayis to feed the solids phase to the intake of a pump, using thecontinuous phase being pumped by the pump to convey the solids phase.There is preferably provided a means for facilitating adding the solidsphase, for example, a funnel or hopper means, or primer chamber.

In the embodiment depicted in FIG. 1, the interior diameter of theacceleration conduit 21 is preferably in the range of from about 1.0inches to about 2.5 inches, most preferably on the order of about 2.0inches. The interior diameter of the waste conduit 18 is preferably inthe range of from about 1.25 inches to about 2.5 inches, most preferablyon the order of about 2.0 inches. The interior diameter of the airconduit 19 (in which the waste conduit 18 is positioned) is preferablyin the range of from about 3.0 inches to about 5.0 inches, mostpreferably on the order of about 4.0 inches, and it is typically atleast about 2 times the diameter of the waste conduit 18.

In accordance with a specific preferred embodiment, the air conduit 19is formed of 3 inch interior diameter stainless steel pipe and is 87.5inches long, the air inlet 22 being 4 inches from the closed end of thepipe; the waste conduit 18 is formed of 1.5 inch interior diametercarbon steel pipe and is 115.5 inches long; the mixing chamber 20 tapersfrom a 3 inch interior diameter at its intake end to a 1.25 inchinterior diameter at its release end and is 3.5 inches long; and theacceleration conduit 21 is formed of 1.25 inch interior diameterstainless steel pipe and is 26.5 inches long.

By providing a waste slurry nozzle in accordance with the presentinvention, there is a sufficient length during which energy exchangetakes place and the mixing chamber and acceleration conduit are shapedsuch that a waste slurry containing solids having at least one dimensionless than about 1/8 inch and solids having no dimension smaller than 1/8inch and no dimension larger than 5/8 inch is accelerated by the air fedthrough the air conduit 19 so that they are travelling at a rate of atleast 75%, preferably close to 100%, of the rate of the air when the airexits from the acceleration conduit 21. The waste slurry nozzleaccording to this invention disintegrates and entrains agglomeratedsolids in the waste slurry. In the embodiment shown in FIG. 1, the flameis co-current with the secondary air from the clinker cooler(s) 14,which is typically travelling at a rate of about 20 miles per hour, sothat the flame is firing down-wind with the gases in the kiln 10. Thesecondary air entering the kiln 10 around the flame is very reactive,thereby providing a high flame speed because relatively little heat isdissipated from the flame to the oxygen and nitrogen in the preheatedsecondary air.

The preferred pressure of the air supplied to the air conduit 19 dependson the geometry of the various elements of the system, and is preferablyin the range of from about 35 psi to about 95 psi, most preferably about65 psi. When employing a waste slurry having a liquid continuous phase,the mass flow rate of air supplied to the air conduit 19 is preferablyin the range of from about 0.20 to about 0.50 weight percent, mostpreferably about 0.24 to 0.25 weight percent, based on the mass flowrate of waste slurry. Preferred air flow rates are in the range of fromabout 280 SCFM (standard cubic feet per minute) to about 800 SCFM, mostpreferably on the order of about 500 ft³ /min. When employing a wasteslurry having a continuous phase which comprises air, the flow rate ofair supplied to the air conduit 19 is preferably in the range of fromabout 700 to about 1500 SCFM.

Preferred waste slurry flow rates are on the order of from about 54lb/min to about 200 lb/min, most preferably about 140 lb/min. The wasteslurry nozzle 16 is preferably designed to accommodate flow up to 360lb/min of waste slurry with 1500 SCFM of air.

The pressure under which waste slurry is supplied to the waste slurryconduit 18 only needs to be sufficient to feed the waste slurry to themixing chamber 20, and it should not exceed the pressure of the airsupplied to the air conduit 19 because if it does, there may be atendency for some of the air to be forced backward.

The end of the acceleration conduit 21 may optionally have a small flameguide to provide a desired adjustment of the width and/or length of theflame.

The ratio between the amount of waste slurry and the amount ofconventional fuel entering the kiln 10 through the waste nozzle 16 andthe conventional fuel nozzle 17, respectively, affects the temperaturegradient within the kiln 10. Conventional fuel has a relatively lowhydrogen content, whereas waste slurry (particularly hazardous wasteslurry) has a relatively high hydrogen content. Because H₂ O producedabsorbs more heat and carries more heat downstream than does CO₂, thetemperature gradient depends on the ratio between the two fuel elementalcomponents. By adjusting the carbon:hydrogen ratio, 80 to 100%substitution of waste slurry fuel for conventional fuel can be achieved.

The various aspects of the various embodiments of the present inventionprovides numerous advantages over the prior art. For example, by burningsome of the solids phase in the flame (i.e., in suspension), severaladvantages can be obtained. First, only about 15% to about 20% of thetotal energy input to a wet process kiln can be input to the calciningzone, and by burning some of the solids in the flame, energy can bereleased in the flame, so that only a portion of the energy resultingfrom the solids is released in the calcining zone. Thus, more energy canbe input using the solids, and more solids can be consumed in the kiln.Second, because heat transfer in the clinkering zone is to materials onthe walls of the kiln, it is important to have a radiant (highlyluminous) flame with much radiant heat--burning solids facilitates thistype of flame.

As an additional example, many advantages are obtained when thecontinuous phase of the waste slurry is liquid instead of, e g., air.First, very frequently, solids are not of high enough BTU content tomaintain high flame speed. Using a liquid continuous phase, a high flamespeed can be maintained. Second, very frequently, solids have a highcarbon hydrogen ratio. A better carbon:hydrogen ratio can be obtainedusing a liquid continuous phase. Third, having the surfaces of solidscovered with liquid material can accelerate ignition and burning of thesolids. Fourth, a much wider selection of solids can be burned whenusing liquid continuous phase than when using air as a continuous phase.

In accordance with a preferred feature of the present invention, thewaste slurry may be prepared by passing a raw waste slurry through apipe grinder as depicted in FIGS. 4-6. The pipe grinder includes firstand third discs 24, 26 splined to a spindle 27, each of the discs 24, 26having holes formed therethrough (as shown in FIG. 5). Positionedbetween the first and third discs 24, 26 is a second disc 25 rotatablymounted on a spacer 28 which is splined to the spindle 27, the seconddisc 25 also having holes formed therethrough (see FIG. 6). The discs24, 25, 26 and the spacer 28 are secured in place between a shoulder 31on the spindle 27 and a cap 33 which is screw-threaded onto the spindle27. The discs 24, 25, 26 abut one another, such that in operation, thereis only a thin film of the material being comminuted between the discs.In operation, the spindle 27 is rotated, together with the first andthird discs 24, 26 and the spacer 28, preferably at a rate of from about80 to about 1750 revolutions per minute. Raw waste slurry is fed, e.g.,by a pump into an inlet chamber 29 adjacent to the first disc 24, passesthrough the holes in the first disc 24, then through the holes in thesecond disc 25, and finally through the holes in the third disc 26,after which it exits through an outlet 30. This treatment reduces thesizes of solids contained in the raw slurry.

The first, second and third discs 24, 25, 26 are positioned within acylindrical housing 32 such that the peripheral surfaces of the discs24, 25, 26 fit snugly within the housing 32. For example, the clearancebetween the peripheral surfaces of the discs and the housing maypreferably be about 50 or fewer thousandths of an inch. The clearance ispreferably smaller than the diameter of the largest particle sizedesired in the effluent from the comminuting apparatus. To reduce theclearance, it is possible to line the housing with any suitablematerial, e.g., ultra high molecular weight polyethylene, available fromHoescht Celanese.

The discs 24, 25, 26 are formed of a material of suitable mechanicalproperties such that they can withstand the conditions to which they aresubjected during comminuting. Such conditions depend, for example, onthe nature, flow rate and pressure of the material being comminuted, therate of rotation of the discs and the sizes of the discs. For example,suitable materials out of which the discs 24, 25, 26 can be constructedinclude steel and other durable metals and alloys, ceramics and polymermaterials. Preferred materials include "workharder" materials, i.e.,materials which become harder as the apparatus is used. Any suitablecoating may be applied to the surfaces of the discs 24, 25, 26, thespindle 27 or the spacer 28 to provide increased durability. Forexample, high molecular weight polymers, e.g., ultra high molecularweight polyethylene (available from Hoescht Celanese), may be used assuitable coatings.

Referring to FIGS. 5 and 6, the discs 24, 25, 26 each have a pluralityof holes (in addition to the one through which the spindle passes)formed through the thickness of the disc. The holes may be of anysuitable shape, and circular holes are preferred. A disc which isupstream relative to a more downstream disc preferably has holes whichare larger than the holes in the more downstream disc. The diameter ofthe holes is preferably in the range of from about 1/4 inch or about3/16 inch to about 21/4 inch. The walls of the holes preferably arestraight (as shown in FIGS. 5 and 6) although it may be suitable toprovide holes which have a slanted shape, curved shape or any othershape. For example, for some applications, it may be desirable toprovide holes which have an acute angle edge at the front surface of adisc (i.e., the surface facing upstream) at the back edge of the holerelative to the direction of rotation of the disc.

Suitable flow rates through the comminuting apparatus vary widelydepending on the nature of the material being comminuted, the pressurewithin the comminuting apparatus, the relative size of the comminutingapparatus and the rate of rotation of the spindle of the comminutingapparatus.

The sizes of the elements in the comminuting apparatus may vary widelydepending on the application for which the apparatus is used. Forexample, for larger flow rates of materials containing large particles,the elements should be relatively larger. The relationship between thesizes of the various elements can also vary widely. The diameter of thediscs (which is usually the same for all of the discs) is preferablyfrom about 6 inches to about 17 inches, which preferably is from about 3to about 5.5 times the diameter of the spindle. The diameter of thespacer is preferably from about 1.25 to about 2 times the diameter ofthe spindle. The thickness of the discs (which may or may not be thesame for all of the discs) is preferably from about 1/8 inch to about3/4 inch.

In accordance with another preferred feature in accordance with thepresent invention, the waste slurry nozzle 16 preferably has a reverseflow mechanism by which any material clogging the nozzle 16 can beforced out through the waste slurry inlet 23 and/or the air inlet 22.

Although the apparatus, slurries and methods in accordance with thepresent invention have been described in connection with preferredembodiments, it will be appreciated by those skilled in this art thatadditions, modifications, substitutions and deletions not specificallydescribed may be made without departing from the spirit and scope ofthis invention as defined in the appended claims.

What is claimed is:
 1. A burner for burning waste, comprising:a conventional fuel nozzle and a waste slurry nozzle, said waste slurry nozzle comprising a first conduit for conveying a waste slurry, a single second conduit for conveying a fluid stream, and an acceleration zone, said acceleration zone comprising a mixing chamber and an acceleration conduit, said first conduit having an inlet and an outlet, said second conduit having an entrance and an exit, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end, said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit, said mixing chamber tapering down from said intake end to said release end and said first conduit outlet and second conduit exit being arranged relative to said mixing chamber intake end such that said waste slurry and fluid streams are mixed in said mixing chamber into a single combined stream.
 2. A burner as recited in claim 1, wherein said first conduit and said acceleration conduit each having a longitudinal axis, said axis of said first conduit and said axis of said acceleration conduit being substantially coaxial.
 3. A burner as recited in claim 1, wherein said first conduit is positioned inside of said second conduit.
 4. A burner as recited in claim 1, wherein said waste slurry nozzle is positioned inside of said conventional fuel nozzle.
 5. A burner as recited in claim 1, wherein said waste slurry nozzle is positioned so as to produce a flow which impinges a flame emanating from said conventional fuel nozzle.
 6. A burner as recited in claim 1, further comprising a kiln having an up end and a down end, said burner being positioned in said down end of said kiln.
 7. A burner for burning waste, comprising a kiln operating at less than atmospheric pressure, said kiln having an up end and a down end, said burner being positioned in said down end of said kiln, the burner comprising:a conventional fuel nozzle and a waste slurry nozzle, said waste slurry nozzle comprising a first conduit, a second conduit, and an acceleration zone, said acceleration zone comprising a mixing chamber and an acceleration conduit, said first conduit having an inlet and an outlet, said first conduit having a substantially linear axis, said second conduit having an entrance and an exit, said second conduit having a substantially linear axis, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end, said acceleration conduit having a substantially linear axis, said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit, said axis of said first conduit and said axis of said acceleration conduit being substantially coaxial, said axis of said second conduit and said axis of said first conduit being substantially parallel.
 8. A burner for burning waste, comprising:a conventional fuel nozzle comprising a first conduit, a second conduit, and an acceleration zone, said acceleration zone comprising a mixing chamber and an acceleration conduit, said first conduit having an inlet and an outlet, said first conduit having an interior diameter in the range of from about 1.0 to about 2.5 inches, said first conduit being positioned inside said second conduit, said second conduit having an entrance and an exit, said second conduit having an interior diameter in the range of from about 3.0 to about 5.0 inches, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end, said acceleration conduit having an interior diameter in the range of from about 1.0 to about 2.5 inches, said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit.
 9. A burner as recited in claim 8, wherein said first conduit has a substantially linear axis, said acceleration conduit has a substantially linear axis, said axis of said first conduit and said axis of said acceleration conduit being substantially coaxial.
 10. A burner as recited in claim 8, further comprising a kiln having an up end and a down end, said burner being positioned in said down end of said kiln.
 11. A waste slurry nozzle, comprising:a first conduit having an inlet and an outlet, a second conduit having an entrance and an exit, and an acceleration zone comprising a mixing chamber and an acceleration conduit, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end; said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit; said acceleration zone being of a length in the range of from about 10 to about 30 times an interior diameter of said acceleration conduit.
 12. A nozzle as recited in claim 11, wherein said mixing chamber is tapered between said intake end of said mixing chamber and said release end of said mixing chamber, the ratio of the difference between the cross-sectional areas of said intake end and said release end, divided by a distance between said intake end and said release end being in the range of from about 0.5 to about 2.0.
 13. A nozzle as recited in claim 11, wherein said first conduit is positioned inside of said second conduit.
 14. A nozzle as recited in claim 11, wherein said air conduit is 3 inch interior diameter steel pipe and is about 87.5 inches long, said waste conduit is 1.5 inch interior diameter steel pipe and is about 115.5 inches long, said mixing chamber tapers from a 3 inch interior diameter at said intake end to a 1.25 inch interior diameter at said release end, said mixing chamber is about 3.5 inches long, and said acceleration conduit is 1.25 inch interior diameter steel pipe and is about 26.5 inches long.
 15. A waste slurry comprising a continuous phase and a solids phase, said solids phase consisting essentially of waste solids having at least one dimension less than about 1/8 inch and waste solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch.
 16. A waste slurry as recited in claim 15, wherein said slurry comprises hazardous waste.
 17. A waste slurry as recited in claim 15, wherein said solids having at least one dimension less than about 1/8 inch are selected from the group consisting of plastics, paint containers with their contents, semisolid paint heels, skins from the tops of containers, semi-solid adhesives, resins, copolymers that are either fully or partially reactive, epoxies, urethanes, acrylics, and polyesters.
 18. A waste slurry as recited in claim 15, wherein said solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch are selected from the group consisting of ground, fully reacted resins, and rims from plastics drums which have been shredded.
 19. A waste slurry as recited in claim 15, wherein said solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch are substantially spherical.
 20. A waste slurry as recited in claim 15, wherein said continuous phase is liquid.
 21. A waste slurry as recited in claim 15, wherein said continuous phase is air.
 22. A waste slurry as recited in claim 21, wherein said air comprises from about 50 to about 225 weight percent of said waste slurry, based on the amount of said solids phase.
 23. A method for burning waste, comprising:feeding a slurry of cement raw materials to an up end of a rotating kiln having said up end and a down end, a calcining zone between said up end and said down end and a clinkering zone between said calcining zone and said down end; and ejecting a waste slurry from a burner at said down end in said clinkering zone such that a portion of said waste slurry burns in a flame emanating from said burner and the remainder of said waste slurry lands in said calcining zone.
 24. A method as recited in claim 23, wherein said waste slurry comprises a liquid continuous phase and a solids phase.
 25. A method as recited in claim 23, wherein said waste slurry comprises a continuous phase and a solids phase, said continuous phase comprising air.
 26. A method as recited in claim 23, wherein said waste comprises hazardous waste.
 27. A method as recited in claim 23, wherein said waste slurry comprises a continuous phase and a solids phase, said solids phase comprising solids having at least one dimension less than about 1/8 inch and solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch, substantially all of said solids having at least one dimension of less than about 1/8 inch being burned in said flame, substantially all of said solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch landing in said calcining zone, such that substantially none of said solids phase lands in said clinkering zone.
 28. A method as recited in claim 23, wherein said rotating kiln is a conventional wet cement kiln.
 29. A method as recited in claim 23, wherein said rotating kiln is a dry cement kiln.
 30. A method as recited in claim 23, wherein said burner comprises a conventional fuel nozzle and a waste slurry nozzle.
 31. A method as recited in claim 30, wherein said waste slurry nozzle comprises a first conduit, a second conduit, and an acceleration zone, said acceleration zone comprising a mixing chamber and an acceleration conduit, said first conduit having an inlet and an outlet, said first conduit having a substantially linear axis, said second conduit having an entrance and an exit, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end, said acceleration conduit having a substantially linear axis, said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit, said axis of said first conduit and said axis of said acceleration conduit being substantially coaxial.
 32. A method as recited in claim 31, wherein said acceleration zone is of a length in the range of from about 10 to about 30 times an interior diameter of said acceleration conduit.
 33. A method as recited in claim 31, wherein said mixing chamber is tapered between said intake end of said mixing chamber and said release end of said mixing chamber, the ratio of the difference between the cross-sectional areas of said intake end and said release end, divided by a distance between said intake end and said release end being in the range of from about 0.5 to about 2.0.
 34. A method as recited in claim 31, wherein said waste slurry comprises a continuous phase and a solids phase, said solids phase comprising solids having at least one dimension less than about 1/8 inch and solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch, said waste slurry being fed into said first conduit under a pressure sufficient to feed said waste slurry through said first conduit, air being fed at a pressure of from about 35 to 95 psi through said second conduit, said air accelerating said waste slurry to a velocity of at least 75% of the velocity at which the air exits from said second conduit.
 35. A method as recited in claim 23, further comprising passing air through a clinker cooler positioned below said down end of said kiln so that clinker formed in said clinkering zone flows out of said kiln into said clinker cooler, said clinker cooler comprising means for exchanging heat between said air and said clinker, thereby heating said air and cooling said clinker, and feeding said heated air into said kiln at said down end of said kiln.
 36. A method as recited in claim 23, wherein at least about 50% of said waste slurry burns in said flame.
 37. A method for burning waste, comprising:feeding a slurry of cement raw materials to an up end of a rotating kiln having said up end and a down end, a calcining zone between said up end and said down end and a clinkering zone between said calcining zone and said down end; and ejecting a waste slurry at said down end into said clinkering zone, said waste slurry comprising a continuous phase and a solids phase, said solids phase consisting essentially of waste solids having at least one dimension less than about 1/8 inch and waste solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch.
 38. A method as recited in claim 37, wherein said waste solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch land in said calcining zone.
 39. A method as recited in claim 37, wherein said waste slurry comprises hazardous waste.
 40. A method for burning waste, comprising:feeding a slurry of cement raw materials to an up end of a rotating kiln having said up end and a down end, a calcining zone between said up end and said down end and a clinkering zone between said calcining zone and said down end; and ejecting a waste slurry at said down end in said clinkering zone, said waste slurry comprising a continuous phase and a solids phase, said solids phase comprising solids having at least one dimension less than about 1/8 inch and solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch.
 41. A method for burning waste, comprising:feeding a slurry of cement raw materials to an up end of a rotating kiln having said up end and a down end, a calcining zone between said up end and said down end and a clinkering zone between said calcining zone and said down end; and ejecting a waste slurry at said down end in said clinkering zone, said waste slurry comprising a continuous phase and a solids phase, said continuous phase comprising air, said air comprising from about 50 to about 225 weight percent, based on the amount of said solids phase.
 42. A waste slurry nozzle, comprising:a first conduit for feeding a waste slurry containing solids having at least one dimension less than about 1/8 inch and solids having no dimension less than about 1/8 inch and no dimension larger than about 5/8 inch, said first conduit having an inlet and an outlet, a second conduit for feeding air from a pressure source at a pressure of from about 35 to 95 psi, said second conduit having an entrance and an exit, and an acceleration zone comprising a mixing chamber and an acceleration conduit, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end; said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit; said mixing chamber and said acceleration conduit being shaped such that said waste fed from said first conduit is accelerated by said air fed from said second conduit to a velocity of at least 75% of the velocity at which the air exits from the second conduit.
 43. Waste burning apparatus including a burner cooperating with a combustion chamber operated at less than atmospheric pressure, said burner comprising:a conventional fuel nozzle and a waste slurry nozzle, said waste slurry nozzle comprising a first conduit, a second conduit, and an acceleration zone, said acceleration zone comprising a mixing chamber and an acceleration conduit, said first conduit having an inlet and an outlet, said second conduit having an entrance and an exit, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end, said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit, said mixing chamber tapering down from said intake end to said release end.
 44. A waste slurry nozzle for a burner for burning waste, said waste slurry nozzle comprising:a first conduit, a second conduit, and an acceleration zone, said acceleration zone comprising a mixing chamber and an acceleration conduit, said first conduit having an inlet and an outlet, said second conduit having an entrance and an exit, said first conduit and said second conduit having parallel longitudinal axes, said first conduit outlet being non-concentrically disposed with respect to the second conduit exit, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end, said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit, said mixing chamber tapering down from said intake end to said release end.
 45. A waste slurry nozzle for a burner for burning waste, comprising:a first conduit, a second conduit, and an acceleration zone, said first conduit, but not said second conduit, being coaxially disposed relative to said acceleration conduit, said acceleration zone comprising a mixing chamber and an acceleration conduit, said first conduit having an inlet and an outlet, said second conduit having an entrance and an exit, said first conduit and said second conduit having parallel longitudinal axes, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end, said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit, said mixing chamber tapering down from said intake end to said release end.
 46. A waste slurry nozzle for a burner for burning waste, comprising:a first conduit, a second conduit, and an acceleration zone, said acceleration zone comprising a mixing chamber and an acceleration conduit, said first conduit having an inlet and an outlet, said second conduit having an entrance and an exit, said second conduit exit being on the order of twice as large as said first conduit outlet, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end, said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit, said mixing chamber tapering down from said intake end to said release end so as to define a sloping surface, and said second conduit exit is arranged relative to said mixing chamber intake end such that a stream flowing through said second conduit is deflected by said sloping surface.
 47. A burner for burning waste, comprising:a conventional fuel nozzle and a waste slurry nozzle, said waste slurry nozzle comprising a first conduit, a second conduit, and an acceleration zone, said acceleration zone comprising a mixing chamber and an acceleration conduit, said first conduit having an inlet and an outlet, said second conduit having an entrance and an exit, said mixing chamber having an intake end and a release end, said acceleration conduit having a receiving end and a discharge end, said intake end of said mixing chamber communicating with said outlet of said first conduit and said exit of said second conduit, said release end of said mixing chamber communicating with said receiving end of said acceleration conduit, said mixing chamber tapering down from said intake end to said release end, wherein the ratio of the difference between the cross sectional areas of said intake end and said release end, divided by a distance between said intake end and said release end is in the range of from about 0.5 to about 2.0.
 48. A waste slurry nozzle as recited in claim 44, wherein said first conduit is disposed within said second conduit.
 49. A waste slurry nozzle as recited in claim 45, wherein said first conduit is disposed within said second conduit. 